In recent years, various kinds of information are digitalized with development and spread of computers. As a device for storing such digital data, there is a storage device such as a magnetic tape and a magnetic disk. Because the amount of data that should be stored increases day by day and reaches a huge amount, a mass storage system is required. Moreover, as well as reduction of the cost spent for a storage device, reliability is also required. In addition, it is also required that data can be easily retrieved later. As a result, a storage system that can automatically realize increase of storage capacity and performance, eliminates duplicated storage to reduce a storage cost and has high redundancy is desired.
Under such a circumstance, in recent years, as shown in PTL 1, a content-addressable storage system has been developed. This content-addressable storage system distributes and stores data into a plurality of storage devices and, by a unique content address specified depending on the content of the data, specifies a storage position where the data is stored. Moreover, some of the content-addressable storage systems divide predetermined data into a plurality of fragments and add a fragment as redundant data, and then store these fragments into a plurality of storage devices, respectively.
Later, the content-addressable storage systems as described above can designate a content address to retrieve data, namely, fragments stored in a storage position specified by the content address and restore the predetermined data before being divided from the fragments.
Further, the content address is generated based on a value generated so as to be unique depending on the content of data, for example, a hash value of data. Therefore, in the case of duplicated data, it is possible to refer to data in the same storage location and acquire data of the same content. Consequently, it is unnecessary to store the duplicated data separately, and it is possible to eliminate duplicated recording and reduce the data volume.